1. Field of the Invention
This invention relates to cyanoacrylate adhesive compositions which are improved by being rendered thixotropic and nondripping by incorporation of finely divided organic powders.
2. Description of the Prior Art
Liquid cyanoacrylate compositions have long been known in the art as excellent adhesives. Having achieved wide acceptance in industrial applications, cyanoacrylates have recently made enormous advances in sales in the consumer adhesive market. Various of the inherent characteristics of cyanoacrylates, which caused no particular difficulties in industrial automatic application equipment, have been detrimental to their unqualified acceptance in consumer use.
Chief among these characteristics are (1) the adhesives' relatively low viscosity, causing it to run or drip off the point of application to some undesired point, and (2) its extremely rapid cure speed when catalyzed by small amounts of moisture, as found in human skin. These characteristics have often made cyanoacrylates troublesome and inconvenient to use by unskilled consumers. Accordingly, a cyanoacrylate adhesive composition with controlled flow characteristics and easier applicability, while yet retaining desirably rapid cure speed and bond strength, would be a great boon to the consumer market, as well as to industrial applications where such properties would be advantageous.
A variety of fillers has been incorporated into cyanoacrylate adhesive compositions to bring about certain changes in properties. U.S. Pat. No. 2,794,788 teaches thickening of cyanoacrylate adhesives by dissolving therein quantities of polymeric alkyl cyanoacrylates, as well as other compounds including polyacrylates and methacrylates, and cellulose esters such as acetate, propionate and butyrate.
U.S. Pat. No. 3,836,377 notes among the additional known thickeners polyvinyl ethers such as polyvinylmethyl ether. U.S. Pat. No. 3,692,752 discloses thickened cyanoacrylate solutions containing certain polyether acrylates/methacrylates, acrylic/methacrylic esters of bis(hydroxyalkyl) phosphonic acid derivatives, and acrylic/methacrylic esters of tris(hydroxyalkyl) cyanuric acid derivatives.
The preceding references relate to thickened homogeneous solutions containing organic compounds as thickeners. Various inorganic materials have also been proposed as fillers, which also have the effect of thickening the composition. Thus, U.S. Pat. No. 3,663,501 teaches preparation of a dental cement containing inert, finely-divided solids such as fused silica, quartz and alumina. Similarly, U.S. Pat. No. 3,607,542 teaches the preparation of a water-resistant cyanoacrylate paste containing insoluble, inert fillers such as salts of calcium, titanium, zinc, tin, aluminum, iron and cooper, among others.
None of the known references relates to use of certain finely-divided organic powders which are not dissolved or not fully dissolved in the cyanoacrylate monomer and which convert the liquid cyanoacrylate to a non-drip, thixotropic gel or paste.